A fuel cell is an electrochemical device for directly converting chemical energy to electricity with higher efficiency than that of mechanical generators. A rapidly expanding need for electric power sources has stimulated the worldwide research and development of fuel cells for transportation, portable computer, cellular phone and various electronic devices. Typically, a fuel cell is assembled using a 2-electrode configuration. The cathode, or positive electrode, is coated with a catalyst for oxygen reduction. The anode is coated with a catalyst for fuel oxidation. An electrolyte, between the cathode and the anode, provides ionic conductivity for ion transport, and induces the electrochemical reactions at the electrode/electrolyte interface.
A fuel cell generally uses liquid or gaseous fuel, such as alcohol or hydrogen. In a hydrogen fuel cell, the electrode reactions is:
At the anode,2H2→4H++4e−E0 =0.0V   (1)
At the cathode,O2+4H++4e−→2H2OE0=1.23V   (2)
The overall reaction is,2H2+O2→2H2OE0cell=1.23V   (3)
An electro-oxidized molecule of hydrogen generates two protons and two electrons. Meanwhile, a molecule of oxygen is electro-reduced by receiving four electrons. The electro-reduced molecule of oxygen combines with 4 protons to form two molecules of water. The theoretical cell voltage of such a fuel cell is 1.23 V. However, because of slow kinetic rate and high over potential for oxygen electro-reduction, the actual cell voltage is only 1.0 V in open circuit, and 0.75 V in operational status.
In an alcohol fuel cell, such as a direct methanol fuel cell, the electrode reaction is:
At the anode,CH3OH+H2O═CO2+6H++6e−E0=0.02V   (4)
The overall reaction of a methanol fuel cell is,
                                                        CH              3                        ⁢            OH                    +                                    3              2                        ⁢                          O              2                                      =                                            CO              2                        +                          2              ⁢                              H                2                            ⁢              O              ⁢                                                          ⁢                              E                cell                0                                              =                      1.21            ⁢                                                  ⁢            V                                              (        5        )            
An electro-oxidized molecule of methanol generates one molecule of carbon dioxide, six protons and six electrons. The theoretical voltage for a methanol/oxygen fuel cell is 1.21V. However, due to very slow kinetics and high over potential of methanol electro-oxidation, such a fuel cell has only 0.7 V for open circuit voltage and 0.4 V in operational status. Furthermore, the greatest challenge for direct alcohol fuel cell is fuel crossover from the anode to the cathode, leading to cathode depolarization, decreasing overall fuel cell's voltage and lowering fuel efficiency. Fuel crossover is a greater problem with increasing fuel concentration. In order to reduce fuel crossover, generally, a fuel cell can use only very low concentration of fuel, for example, less than 1 M for a methanol fuel cell.
Therefore, the inventors have provided an improved fuel cell for generating hydrogen gas, electrical power and mediation of electrochemical reactions and reactant transport.